Not applicable
In inventing a propeller drive for a human powered boat, the initial impulse would be to use a rope or belt. Indeed, this approach has been picked up on in the development of human powered boat drive systems at least as far back as Victorian times as represented in 1869 with Ross (U.S. Pat. No. 98,302), 1889 with Frenzel (U.S. Pat. No. 397,282), as well as by others including Storms, (U.S. Pat. No. 621,465), Mosteller (U.S. Pat. No. 1,072,027), Szafka (U.S. Pat. No. 1,411,540), Avellino (U.S. Pat. No. 3,182,628), Shiraki (U.S. Pat. No. 5,194,024), Parant (U.S. Pat. No. 5,362,264), Avvocato (France 1,375,350), _Lackner (Germany 2,226,178) . The fact that even though a toothed belt may be used as in White (5,547,406 et el), Lekhtman (U.S. Pat. No. 6,231,408), Marinc (U.S. Pat. No. 5,580,288), et el, doesn""t ease the condition of energy loss due to deforming soft material as it engages into and twists around a pulley. This type of system absorbs too much of the cyclist""s energy to actuate it. Furthermore, in higher torque situations, ropes or belts will tend to slip. Toothed belts can be built large enough by those trained in the art to prevent slippage with medium-high torque propellers, but by the time this problem has been solved, he material deformation energy loss as the drive is actuated will have been way too high. This fact can be further proven in that although belts and toothed belts have been around for a long time, their use has still not caught on in bicycles.
In 1984, a pedal powered watercraft called the Flying Fish was the first known hydrofoil to achieve successful flight under human power (IHPVA, 1984). It had broken most national and international speed records from the 100 meter sprint to the 2000 meter (SCIENTIFIC AMERICAN, 1986). The strut and drive system consisted of a drive shaft in the plane of the pedal crank connected to a propeller shaft by a #25 or xc2xc pitch chain twisted into a xe2x80x9cmobiusxe2x80x9d, and engaged to a driven propeller shaft sprocket below and whose plane of rotation was twisted a quarter turn away. Examples are also to be found in Hoffman 1982 (U.S. Pat. No. 4,349,340), Eide 1991 (U.S. Pat. No. 5,011,441), Parant 1994 (U.S. Pat. No. 5,362,264), et el.
Due to the fact that the Flying Fish chain was operated near its breaking point, it spun easily, but could only be used in racing. Also the Flying Fish type setup used secondary shafting which means two or more chains. Other prior art which also includes the use of secondary shafts is exemplified in Marangoni (U.S. Pat. No. 1,701,381), Maranic (U.S. Pat. No. 5,580,288), White (U.S. Pat. No. 5,547,406, et el), Kasper (U.S. Pat. No. 5,651,706), Grundner (Swiss 23,067), (Germany 10,338) et el. Although this characteristic allows for easy pulley diameter/gear ratio change adaptation, it is heavier, more complex because of more moving parts, requires extra power to operate the extra shaft, chain/belt and bearings, and is extremely difficult to maintain the tension of both or more belts or chains.
Although Eide (U.S. Pat. No. 5,011,441), et el simplify the drive over those using secondary shafting to the use of just two shafts, reliability problems were present due to derailing and/or chain breakage. Although the drive unit of Eide et el would provide chain operation with low power loss in a twisted environment, it would often prematurely break due to the chain not being heavy duty enough as well as operating in a continually loosening or loosening and sometimes tightening situation. For those and other reasons, chains, and ultimately sprockets would wear out faster.
Attempts to solve the problem of chain tensioning included drive units with adjustable fixed idler systems that could be unbolted, relocated, then retightened. These attempts started in the human powered boat racing efforts of this inventor pre-1992; Bill Murphy, Paul Niedermann, Warren Beauchaump, Bob Buerger pre-1998, et el, and an example is to be found in Gauthier (U.S. Pat. No. 5,672,080)
In a non constantly tensioned system, if a single bolted idler or jack shaft were to get repositioned, or if the drive system was to experience a chain which lengthens, the system will jam, skip or undergo teething problems. Chains lengthen or xe2x80x98stretch xe2x80x99 due to initial breaking in, temperature changes, wear, etc. A constant vigil must therefore be kept on anything other than self-tensioning drive in order for the system to work properly.
Newer type bicycle chains (#43; xc2xd k pitch) are currently available on the market that lend themselves to being operated while twisted. There are now available full size bicycle chain types that can be twisted 90 degrees over a distance of some 18 inches or less. This development allows full size chain to be used in struts almost as narrow as they would need to be for the thinner lighter duty chain. Bicycle chain has 2 to 2.5 times larger tensile strength than #25
It is absolutely essential that the drive unit be able to provide the MOST TORQUE POSSIBLE with the LEAST OPERATIONAL DRAG POSSIBLE.
If propellers were analyzed for drag where they do the most lifting, (average=0.8xc3x97[propeller tip diameter]) it would be found that the faster the rotational velocity, the more drag there is. The extreme would be where there""s infinite velocity, no advance, and therefore infinite surface drag. This is due to the increased surface friction of the higher revving propellers, and is arrived at by the equation:   Fd  =            Cd      ⁡              (                  1          2                )              ⁢    ρ    ⁢          xe2x80x83        ⁢          V      2        ⁢    S  
where Fd=drag; Cd=drag coefficient [constant]; [xc2xd xcfx81 cancels out near the water surface] xcfx81 is density (xc2xd xcfx81 cancels out near the water surface in English units); and note here: V=velocity and its squared!; S=surface area.
On blade angles, the formula that applies is       V    ⁡          (      final      )        =            V      ⁡              (        boat        )                    sin      ⁡              (        β        )            
where V(final)=blade velocity, V(boat)=boat velocity; B=blade angle at a particular diameter. Suffice it to say that the lesser angle B is, the faster the blade element has to go in order to get the same advance.
The full proof is very long, but the general idea is that when the velocity increases, drag force increases to the square!
Therefore, slower turning propellers with higher pitch to diameter ratios have less drag, but the bad news is that they have increased torque. The extreme is where there""s zero velocity, infinite advance, and, of course, infinite torque.
My invention is the first hydrodynamically low drag daggerboard type drive that is intended for use with regular size bicycle chain. It can withstand two and a half times as much torque as those units that employ #45 xc2xc inch pitch chain.
Concerning dependability, a user of a pedal powered drive unit will want to spend as little time as possible fixing, tinkering and adjusting the unit and the most time pedaling out on the water. My invention promotes this in that it is the first pedal powered drive that has a self-tensioner; in other words, as the length of the chain varies, the tensioner ADAPTS to it! The tensioner keeps the chain under tension regardless of its length. Chains will stretch due to eventual wear, but more likely because of factors like frictional heat, even temperature change. My invention solves the reliability problem by constantly tensioning the chain in a way somewhat similar to a regular rear-wheeled-tensioned multi speed bicycle, except in three dimensions instead of substantially two.
In order to prevent the chain from derailing (as well as have the lowest drag as possible), idlers must each be parallel to the pivot plane of the chain, perpendicular to path of the chain pin/roller axis. Therefore, in a twisted chain drive, they must be tilted the same degree as the twist. The leeward idlers in this invention are all matched up to the twist in three dimensions, and each idler and sprocket is surrounded by guide plates to further prevent derailing.
Therefore, It is the object of this invention to provide a rugged durable lightweight compact human powered boat drive system that lends itself to installation as a kick-up daggerboard, that lends itself to a multihull installation, an economical installation, a high performance installation, an integrated human powered hydrofoil strut installation, a high torque (large propeller pitch) installation, or any combination of the above.
It is another object of this invention to provide a self-tensioning drive system wherein it requires less adjustment, maintenance,
It is another object of this invention to provide a drive system that can be framed in as a one-piece jacket that supports the pedal crank bracket and hardware in an accessible fashion above the waterline, and houses the propeller shaft mount, chainpath, internally in a smooth faired streamlined case below the water.
It is further an object of this invention to provide a drive system that is entirely maintenance free, and wherein the entire drive system lends itself to being totally waterproof wherein the interior workings may be non-corrosion-resistant, and therefore of lesser expense.
It is another object of this invention to provide a drive with a narrower strut, and therefore faster speeds.
Other objects of this invention will become obvious upon further examination.